Just a handy site I picked up while hunting out a PS4 - it is also useful for other in-demand items that are mostly out of stock.

http://www.nowinstock.net/ basically screen-scrapes a bunch of online retailers for particular items. With it you can set different alerts (e.g. email, browser flashing/audio) when the given item is in stock so you can snap it up quickly.

I found this invaluable while hunting out a PS4. For those of you similarly nerdy enough to want another item early after release, check the site out.